The present invention relates generally to disk drives and, more particularly, to a disk drive employing adaptive feed-forward vibration compensation to enhance a retry operation.
Vibrations affecting the actuator arm in a disk drive degrade the performance of the recording/reproduction process. The errors induced by the vibrations may exceed the correction power of the sector level error correction code (ECC). When this happens, the disk drive typically executes a retry operation wherein predetermined parameters (e.g., read channel parameters) are xe2x80x9cfine tunedxe2x80x9d before attempting to reread the sector. The disk drive may execute several retries while varying the parameters until the sector is successfully recovered. The likelihood of successfully recovering a sector depends on the flexibility of the system to achieve the necessary signal-to-noise ratio (SNR) to enable recovery of the sector. To this end, it is desirable to xe2x80x9cfine tunexe2x80x9d several aspects of the recording/reproduction process so that several attempts can be made to recovery a sector before declaring it unrecoverable.
The present invention may be regarded as a disk drive comprising a disk having a plurality of tracks. The disk drive further comprises a head, and an actuator responsive to an adjusted control effort signal for actuating the head radially over the disk. The disk drive includes a servo control system for generating the adjusted control effort signal. The servo control system comprises a position error generator for generating a position error signal indicative of the head""s position with respect to a centerline of a selected track. The servo control system further comprises a servo compensator, responsive to the position error signal, for generating a nominal control effort signal, and sensor for sensing a vibration affecting the disk drive to generate a sensor signal. An adaptive vibration compensator, responsive to the sensor signal, generates a feed-forward signal. A signal generator combines the nominal control effort signal with the feed-forward signal to generate the adjusted control effort signal applied to the actuator. During a normal read operation the adaptive compensator is disabled to substantially remove the contribution of the feed-forward signal from the adjusted control effort signal, and during a retry read operation the adaptive compensator is enabled to include the contribution of the feed-forward signal in the adjusted control effort signal.
In one embodiment, the disk drive further comprises a plurality of programmable parameters. During a first number of disk revolutions of the retry read operation the disk drive modifies the programmable parameters with the adaptive vibration compensator disabled. During a second number of disk revolutions of the retry read operation the disk drive enables the adaptive vibration compensator. In one embodiment, the adaptive vibration compensator comprises a programmable closed-loop parameter, and during the second number of disk revolutions the disk drive adjusts the closed-loop parameter.
In another embodiment the disk drive disables a normal write operation if the sensor signal exceeds a predetermined threshold.
The present invention may also be regarded as a method of enhancing a retry read operation in a disk drive comprising a disk having a plurality of tracks, a head, an actuator responsive to an adjusted control effort signal for actuating the head radially over the disk, and a servo control system for generating the adjusted control effort signal. A position error signal indicative of the head""s position with respect to a centerline of a selected track is generated, and a nominal control effort signal is generated from the position error signal. A vibration affecting the disk drive is sensed to generate a sensor signal, and a feed-forward signal is generated in response to the sensor signal. The feed-forward signal is combined with the nominal control effort signal to generate the adjusted control effort signal. During a normal read operation, the contribution of the feed-forward signal is substantially removed from the adjusted control effort signal,.and during a retry read operation, the contribution of the feed-forward signal is included in the adjusted control effort signal.